When molecules and morphology work together: lines of evidence for the validity of Caridina buehleri Roux (Crustacea :Decapoda : Atyidae) and for C. gueryi Marquet, Keith and Kalfatak as its junior synonym

The taxonomy of the freshwater shrimps Caridina (Atyidae) is very complex and confused mostly because the morphological characters that have traditionally been used for species delimitation and identification are highly plastic. There is thus a need for an integrative approach to their taxonomy. In total, 42 specimens belonging to either Caridina buehleri Roux, 1934 or Caridina gueryi Marquet, Keith & Kalfatak, 2009 were examined. We combined here morphological data from 12 specimens from the whole distributional range of the species, including type specimens with 16S mtDNA analyses from seven freshly sampled specimens, to verify the specific status of Caridina buehleri from Papua New-Guinea, Central Sulawesi, Western Samoa and the Solomon Islands, and C. gueryi from Vanuatu. The comparison of 24 morphological characters showed that morphological variations of character traits between C. gueryi and C. buehleri are widely overlapping and that no morphological feature can effectively split specimens into two clear groups. Molecular characters corroborated these results, as specimens from both groups were only separated by a 2% p-distance, a genetic distance that is coherent with their potentially high dispersal abilities. We thus consider C. gueryi as a junior synonym of C. buehleri. Finally, C. buehleri is characterised mainly by a styliform and characteristically indented rostrum and a long stylocerite. Detailed re-descriptions of the type specimens of C. buehleri and C. gueryi are given, as well as their geographical and ecological distribution.